• Applied Science and Convergence Technology
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• v.24 no.4
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• pp.96-101
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• 2015

Quantitative evaluation of photocatalytic activity of oxide nanoparticles in aqueous solution is quite challenging in that the kinetic reaction rate is determined by a complicated interplay among various limiting factors such as light scattering and absorption, diffusion and adsorption of reactants in condensed liquid phase, photoexcited charge separation and recombination rate, and the exact nature of active sites determined by detailed morphology and crystallinity of nanocrystals. Here, we present our simple experimental results showing that the kinetic regime of a typical photocatalytic degradation experiment over UV-irradiated $TiO_2$ nanoparticles in aqueous solution is in that dominated by the photoactivity of $TiO_2$ and its concentration. This result lays a firm ground of using the measured kinetic reaction rate in evaluating photocatalytic efficiency of oxide nanocrystals under evaluation.

• Journal of the Semiconductor & Display Technology
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• v.22 no.1
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• pp.118-123
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• 2023

Partially magnetized capacitively coupled plasma (CCP) sources are investigated using a two-dimensional kinetic simulation code named EDIPIC-2D. A converging numerical solution was obtained for CCP with a 60 MHz power source, while properly capturing the dynamics of electrons and power absorption over a single RF period. The effects of magnetic fields with different orientations were evaluated. Axial magnetic fields caused changes in the spatial distribution of plasma density, affecting the loss channel. Transverse magnetic fields enhanced stochastic heating near the powered electrode, leading to an increase in plasma density while the significant E×B drift loss compensated for this rise.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.20 no.4
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• pp.371-382
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• 2022

Carbonates are inorganic ligands that are abundant in natural groundwater. They strongly influence radionuclide mobility by forming strong complexes, thereby increasing solubility and reducing soil absorption rates. We characterized the spectroscopic properties of Am(III)-carbonate species using UV-Vis absorption and time-resolved laser-induced fluorescence spectroscopy. The deconvoluted absorption spectra of aqueous Am(CO₃)₂^- and Am(CO₃)₃^3- species were identified at red-shifted positions with lower molar absorption coefficients compared to the absorption spectrum of aqua Am³⁺. The luminescence spectrum of Am(CO₃)₃^3- was red-shifted from 688 nm for Am³⁺ to 695 nm with enhanced intensity and an extended lifetime. Colloidal Am(III)-carbonate compounds exhibited absorption at approximately 506 nm but had non-luminescent properties. Slow formation of colloidal particles was monitored based on the absorption spectral changes over the sample aging time. The experimental results showed that the solubility of Am(III) in carbonate solutions was higher than the predicted values from the thermodynamic constants in OECD-NEA reviews. These results emphasize the importance of kinetic parameters as well as thermodynamic constants to predict radionuclide migration. The identified spectroscopic properties of Am(III)-carbonate species enable monitoring time-dependent species evolution in addition to determining the thermodynamics of Am(III) in carbonate systems.

• Advances in environmental research
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• v.4 no.2
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• pp.119-133
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• 2015

Water pollution means that the physical, chemical and biological properties of water are changing. In this study, adsorption was chosen as the treatment method because it is an eco-friendly and low cost approach. Magnetite is a magnetic material that can synthesize chemical precipitation. Magnetite was used for the removal of copper in artificial water samples. For this purpose, metal removal from water dependent on the pH, initial concentration of metal, amount of adsorbent and effect of sorption time were investigated. Magnetite was characterized using XRD, SEM and particle size distribution. The copper ions were determined by atomic absorption spectrometry. The adsorption of copper on the magnetite was studied in a batch process, with different aqueous solutions of Cu (II) at concentrations ranging from 10 to $50mg\;l^{-1}$. Optimum conditions for using magnetite were found to be concentration of $10mg\;L^{-1}$, pH: 4.5, contact time: 40 min. Optimum adsorbent was found to be 0.3 gr. Furthermore, adsorption isotherm data were analyzed using the Langmuir and Freundlich equations. The adsorption data fitted well with the Freundlich ($r^2=0.9701$) and Langmuir isotherm ($r^2=0.9711$) equations. Kinetic and equilibrium aspects of the adsorption process were studied. The time-dependent Cu (II) adsorption data were described well by a pseudo-second-order kinetic model.

• Journal of the Korean Chemical Society
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• v.38 no.11
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• pp.792-799
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• 1994

The spectral changes of 3,3'-diethyl oxacarbocyanine(DOC) in the aqueous solution and in the presence of polyacrylic acid(PAA) were studied by means of absorption and fluorescence spectroscopy. The spectral change of DOC in the aqueous solution with concentration changes is attributed to the formation of dimer. In the presence of PAA, the characteristic changes of metachromatic band with changes of P/D (the ratio between available binding site and the dye concentration) are found and the discussions are made in terms of stacking theory. A kinetic study of the interaction between DOC and PAA was also investigated by the absorption and fluorescence stopped-flow spectroscopy. The observed relaxation effect in PAA-DOC system can be described quantitatively by assuming two relaxation processes occur.

• Journal of the Korean Chemical Society
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• v.39 no.8
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• pp.604-610
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• 1995

The interaction between 3,3'-dipropyl oxacarbocyanine and poly(styrenesulfonate) has been studied by means of absorption and fluorescence spectroscopic methods. The results was interpreted by stacking model. The kinetic studies of the interaction between 3,3'-dipropyl oxacarbocyanine and poly(styrenesulfonate) were carried out by the absorption and fluorescence spectroscopic stopped-flow methods. The observed relaxation effect in DPC-PSS system was described quantitatively by assuming two relaxation processes. The dependence of rate of reaction on the salt concentration of the solution was also studied. The results are consistent with the two-step mechanism.

• Journal of the Korean Chemical Society
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• v.20 no.3
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• pp.193-197
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• 1976

The ultrasonic absorption has been measured in aqueous solution of dodecyl pyridinium chloride (DPC) at $20^{\circ}C$ over the frequency range of 0.1${\sim}$90 Mc.The excess absorption was observed only in solutions in which the concentration was higher than the critical micellar concentration(cmc). The mechanism for this feature was attributed to the reaction $M_2\;{\rightleftharpoons}\;M_1\;＋\;1.2Cl^-$ Where $M_2$ and $M_1$ and M1 are two types of micelle. The rate constants of the forward and the reverse reactions were $6.6{\times}10^5 sec^{-1}\;and\;2.7{\times}10^11sec^{-1}mol^{-1.2}$respectively. Some kinetic charateristics including the free energy, enthalpy and entropy were calculated.

• Journal of Energy Engineering
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• v.14 no.3 s.43
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• pp.194-202
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• 2005

The present study was analytically and experimentally carried out to predict the absorption characteristics on combined heat and mass transfer process in a vertical falling film of variable absorbers. Heat and mass transfer enhancements were analytically investigated. Effects of geometric parameters by insert device (spring) and corrugate, flow pattern on absorption performances has been also investigated. Especially, the optimal values of absorber geometry (ID=22.8mm, L=1150m) and kinetic variables (solution flow rate, flow pattern) for maximum absorption performance has been predicted by the numerical analysis. The maximum absorption performance in a numerical analysis and experiment was shown at the wavy-flow by insert device (spring).

• Journal of Hydrogen and New Energy
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• v.15 no.3
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• pp.250-256
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• 2004

Magnesium and its alloys have the high potential as hydrogen storage materials because of their highest hydrogen storage capacity, low density and abundant resources. But poor kinetic properties of hydriding and dehydriding and high working temperature have limited their practical applications. In this study, the Mg-Ni binary alloys with different amount of Ni were produced by gravity casting and characterized in order to investigate the relationship between the microstructures and hydriding properties. The maximum hydrogen absorption capacity decreased, but the absorption kinetics increased with Ni content. The difference in the absorption kinetics was resulted from the differences in the sort and shape of primary solid phases and eutectic microstructure.

• Nutrition Research and Practice
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• v.8 no.5
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• pp.550-557
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• 2014

BACKGROUND/OBJECTIVES: Angelica keiskei is a green leafy vegetable rich in plant pigment phytochemicals such as flavonoids and carotenoids. This study examined bioavailability of flavonoids and carotenoids in Angelica keiskei and the alteration of the antioxidant performance in vivo. SUBJECTS AND MATERIALS: Absorption kinetics of phytochemicals in Angelica keiskei were determined in healthy older adults (> 60 y, n = 5) and subjects with metabolic syndrome (n = 5). Subjects consumed 5 g dry Angelica keiskei powder encapsulated in gelatin capsules with a low flavonoid and carotenoid liquid meal. Plasma samples were collected at baseline, 0.5, 1, 2, 3, 4, 5, 6, 7, and 8 h. Samples were analyzed for flavonoids and carotenoids using HPLC systems with electrochemical and UV detection, respectively, and for total antioxidant performance by fluorometry. RESULTS: After ingestion of Angelica keiskei increases in plasma quercetin concentrations were observed at 1-3 and 6-8 hr in the healthy group and at all time points in the metabolic syndrome group compared to baseline (P < 0.05). Plasma lutein concentrations were significantly elevated in both the healthy and metabolic syndrome groups at 8 hr (P < 0.05). Significant increases in total antioxidant performance were also observed in both the healthy and the metabolic syndrome groups compared to baseline (P < 0.05). CONCLUSIONS: Findings of this study clearly demonstrate the bioavailability of phytonutrients of Angelica keiskei and their ability to increase antioxidant status in humans.